Introduction
Regex Tester takes a pattern and a test string, runs them through JavaScript's built-in RegExp engine, and shows you exactly which characters matched, which capture groups fired, and where every match starts and ends. Patterns rarely work the first time — they need to be tried against real samples, tweaked, tried again — and this tool keeps that loop tight: type, edit, see the result, repeat.
Regular expressions are still the fastest way to pull structured pieces out of messy text: email addresses in a log dump, UUIDs in a JSON blob, timestamps at the start of every line. Writing one correctly depends on small details — anchors, greedy versus lazy quantifiers, escape rules — and those details are much easier to spot when the engine highlights your mistakes in real time instead of failing silently later inside a script.
Everything runs locally in your browser. Patterns, test strings, and match results never leave the tab, which matters when the sample data includes production log lines, customer records, or anything else you would rather not paste into a server-side tester.